The reverse of the 20 cent coin was redesigned to removed the kiwi, since the "kiwi dollar" now portrayed that bird. The new reverse design, by Robert Maurice Conly, featured the well-known Māori carving depicting Pukaki, a chief of the Ngāti Whakaue iwi (tribe) of Te Arawa.

This bimetallic version of the coin was included in mint sets in 1994 only.

New Zealand briefly considered making the 50 cents a bimetallic coin. However, it was decided that the low face value of the coin meant that it would not be worthwhile. However, they did include a version of the coin in sets only, in 1994, and it is a beautiful coin indeed.

When New Zealand went decimal, the 5 cents, 10 cents and 20 cents coins had retained the size and weight of their predecimal counterparts, the sixpence, shilling and florin respectively. As time passed, they came to seem too large and heavy for their worth, as did the 50 cents coin also. New Zealand therefore decided to demonetise the 5 cents coins and reduce the size of the other three coins.

From Wikipedia:

On 11 November 2004, the Reserve Bank announced that it proposed to take the 5c coin out of circulation, and to make the existing 50, 20 and 10c coins smaller and use plated steel to make them lighter. The reasons given were:

The 5c coin was now worth a third of what a cent was worth back in 1967, when New Zealand decimalised its currency. Surveys had found that 50, 20 and 10c coins were too large and could not be easily carried in large quantities. The original 50c coin, with a diameter of 3.2 centimetres, was one of the largest coins in circulation worldwide, and the original 20c coin, New Zealand's second biggest coin at the time at 2.8 cm, is bigger than any current circulating coin (the biggest coin in circulation is the $2 coin at 2.6 cm).

The size of the 10c piece was too close to that of the dollar - in fact, it was so close that it was possible to put two 10c pieces in a parking meter together and receive $1 worth of parking time, or jam the meter and make parking free anyway. The advent of pay and display metering in larger cities, whereby one is required to use another meter if the first one is jammed, has largely stopped this practice.

The prices of copper and nickel used to mint the old coins were high and rising steeply, and the metal content of some coins exceeded their face value.

After a three-month public submission period that ended on 4 February 2005, the Reserve Bank announced on 31 March it would go ahead with the proposed changes. The changeover period started on 31 July 2006, with the old coins usable up until 31 October 2006. The older 50, 20, 10 and 5c pieces are no longer legal tender, but are still redeemable at the Reserve Bank.

In August 2005, the Royal Canadian Mint, which has minted Canadian coins in plated steel in the past, was selected by the Reserve Bank to make the new coins. The new coins have a unique electromagnetic signature which enables modern vending machines to determine coin counterfeiting and foreign coins, and it was estimated the changeover would remove nearly $5 million of foreign coinage from circulation.

The change to smaller coins is also advantageous to Australia, as the outgoing 5, 10, and 20c coins were of the same size and weight as Australian coins of these denominations, and were easily confused by shopkeepers and retailers, as well as being usable in Australian vending machines and parking meters.

On 31 July 2006 the new coins were released. The 10 cents coin retained the same reverse design, but it was now made of copper-plated steel. It was smaller and lighter, being 20.5 mm in diameter and weighing 3.3 grams.

On 31 July 2006, the new 20 cent coin was released alongside the new 10 cent and 50 cent coins as part of the Reserve Bank's "Change for the better" silver coin replacement. The new 20 cent coin had the same reverse as the 1990 to 2006 minted coins and the same obverse as the 1999-onward coins, but the coins were reduced in size. The new 20 cent coins are made of steel, covered in a layer of nickel, copper, then nickel again. The new coins are 21.75 mm in diameter and 4 grams in weight. They have Spanish flower milling around the edge, splitting it into seven sections. For their introduction in 2006, 116 million were minted, with a total value of NZ$23.2 million.

The 50 cents coin retained the same reverse design of HMS Endeavour. The coin was now made of nickel-plated steel. It weighed 5 grams and had a diameter of 24.75 mm.

The old coins were legal tender up until 31 October 2006. The older 50, 20, 10 and 5c pieces are no longer legal tender, but are still redeemable at the Reserve Bank. The old sixpence, shilling and florin coins that had remained in circulation was also demonetised as of 1 November 2006.

It was a very bold move of New Zealand to replace three coins at once, but it worked successfully.

That completes my survey of New Zealand's coinage. Any comments, corrections or additions are welcome.

Yes, I agree, the bi-metal 50c is a very nice coin. I got the 1994 set a long time ago to get this coin. Not sure why they were thinking of introducing it though.

My New Zealand trip in March really got me into New Zealand coins. Whilst I was there I got the following:

1988 set (as it was the last to include 1c and 2c coins)1989 set (the last to include the Kiwi 20c)2006 set (the last to contain the 5c and large size 10c, 20c and 50c)

I already had the 1994 and 1990 sets, the latter including the first $1 and $2 coins and new-design 20c.

A consequence of the re-sizing is that Australian coins can no longer find their way into New Zealand circulation. Old New Zealand coins (5c, 10c and 20c) can and do still circulate in Australia.

Although the kiwi 20c design was replaced in 1990, it was apparently still more common than the newer design when the coins were withdrawn in 2006. The re-issue meant that all 20c coins carried the same design for the first time since 1990.

I still donít like the new 10c. The others are fine but I just donít like coins changing to a copper-colour, particularly when the coins are just plated. I know itís good practice to have coins in different colours, but to me it just makes them seem more worthless than ďsilversĒ.

They are nice coins to collect. I'm not keen on the kotuku as a design, though - it leaves too much space towards the bottom of the coin.

The 10 cents changing to "red" - well, it's an acknowledgement of its lower spending power. Traditionally the lowest denominations in NZ were red. Also, the more differences between coins (colour being one of them), the easier it is to differentiate between them.